Phase current measurement is part of a measurement scheme in a poly-phase (e.g., three-phase) electric machine control system operating in a torque control mode that utilizes current measurement signals in a current control feedback loop. Conventional control systems for multi-phase electric machines, such as permanent magnet synchronous machines (PMSMs), typically utilize a Park transformation or a similar mathematical transformation to convert the measured phase currents in the alternating current (AC) frame (stator reference frame) to the direct current (DC) frame (rotor reference frame, or direct-quadrature (d-q) reference frame) to simplify the control system.
The closed loop current control system operating in the d-q reference frame adjusts the motor voltage command so that the resulting motor current measurement matches the reference motor current command. However, if the measurement of the motor current is incorrect, e.g., due to a large offset error in the phase current measurement, the actual motor current resulting from the adjusted motor voltage will be incorrect. Consequently, this will result in a large motor position dependent torque ripple at the motor shaft. A large torque ripple may produce a motor torque in a direction opposite to the direction of the motor torque command, and it will be difficult to move the motor from specific motor positions. This opposing torque may result in violation of system goals or fault management requirements.